The present invention relates to control of moisture inside a packaged electronic device and relates particularly to highly moisture-sensitive electronic device elements having multiple highly moisture-sensitive electronic devices and methods for their fabrication to prevent premature device failure or premature degradation of device performance.
In manufacturing, electronic devices are typically produced by fabricating large substrates containing multiple electronic devices. These substrates are typically selected from the group consisting of glass, plastic, metal, ceramic, silicon and other semiconductor materials, or combinations of these materials. The substrates may be rigid or flexible and may be handled as individual units or continuous rolls. The primary reason for fabricating multiple electronic devices on large individual substrates or a continuous roll substrate is to reduce manufacturing cost by decreasing handling, increasing throughput, and increasing yield. In the micro-electronics industry silicon wafer processing has increased from 2 inch wafers to 12 inch wafers resulting in significant cost reductions. In the liquid crystal display (LCD) industry glass substrate processing has increased from 300 mmxc3x97400 mm substrates to over 600 mmxc3x97700 mm substrates with the same result. In manufacturing of highly moisture-sensitive electronic devices, such as organic light-emitting devices (OLED), polymer light-emitting devices, charge-coupled device (CCD) sensors, and micro-electro-mechanical sensors (MEMS), the same economies of scale are achieved by fabricating large individual substrates or a continuous roll substrate with multiple highly moisture-sensitive electronic devices. FIG. 1A shows an unencapsulated highly moisture-sensitive electronic device element 14 containing multiple highly moisture-sensitive electronic devices 12 on an individual substrate 10, and FIG. 1B is a schematic sectional view of the highly moisture-sensitive electronic device element 14 taken along section line 1Bxe2x80x941B of FIG. 1A. Fabricating large individual substrates or a continuous roll substrate with multiple highly moisture-sensitive electronic devices, however, introduces a problem that is not important for less moisture-sensitive electronic devices in that highly moisture-sensitive devices must be protected from even short term exposure to moisture during fabrication.
Typical electronic devices require humidity levels in a range of about 2500 to below 5000 parts per million (ppm) to prevent premature degradation of device performance within a specified operating and/or storage life of the device. Control of the environment to this range of humidity levels within a packaged device is typically achieved by encapsulating the device or by sealing the device and a desiccant within a cover. Desiccants such as, for example, molecular sieve materials, silica gel materials, and materials commonly referred to as Drierite materials are used to maintain the humidity level within the above range. Short term exposure to humidity levels greater than 2500 ppm during the fabrication and encapsulation of these types of electronic devices typically does not cause measurable degradation of device performance. For this reason encapsulation of these types of electronic devices is done after the electronic devices are separated from the initial substrate.
In the manufacture of liquid crystal displays the electronics and the liquid crystal materials are not highly moisture-sensitive; therefore, the process for encapsulating the electronics and the liquid crystal materials does not require protection from ambient moisture during fabrication. FIG. 2A shows a typical multiple LCD element 28 before separation into single LCD devices, and FIG. 28 is a schematic sectional view of the multiple LCD element 28 taken along section line 2Bxe2x80x942B of FIG. 2A. In LCD manufacturing the LCD back-plane 22 and the LCD front-plane 24 contain multiple LCD devices. The LCD back-plane 22 and the LCD front-plane 24 are bonded together with a sealing material 20 that surrounds each LCD device except for a gap in the sealing material 20. After fabrication of the multiple LCD element 28 the LCD devices are separated and filled with liquid crystal material. After filling the LCD devices, the gap in the sealing material 20 is sealed with a gap sealing material to retain the liquid crystal material and to protect the LCD back-plane electronics 26 and the liquid crystal material from moisture. Because LCD devices are not highly moisture-sensitive, the separation process of the multiple LCD clement is typically performed in an ambient air environment without protecting the LCD devices from moisture with no measurable degradation of the LCD devices.
Particular highly moisture-sensitive electronic devices, for example, organic light-emitting devices (OLED) or panels, polymer light-emitting devices, charge-coupled device (CCD) sensors, and micro-electro-mechanical sensors (MEMS) require humidity control to levels below about 1000 ppm and some require humidity control below even 100 ppm. Such low levels are not achievable with desiccants of silica gel materials and of Drierite materials. Molecular sieve materials can achieve humidity levels below 1000 ppm within an enclosure if dried at a relatively high temperature. However, molecular sieve materials have a relatively low moisture capacity at humidity levels at or below 1000 ppm, and the minimum achievable humidity level of molecular sieve materials is a function of temperature within an enclosure: moisture absorbed, for example, at room temperature, can be released into the enclosure or package during temperature cycling to higher temperature, such, as, for example, to a temperature of 100xc2x0 C. Desiccants used within such packaged devices include powders of metal oxides, alkaline earth metal oxides, sulfates, metal halides, or perchlorates, i.e. materials having desirably relatively low values of equilibrium minimum humidity and high moisture capacity. However, such materials often chemically absorb moisture relatively slowly compared to the above-mentioned molecular sieve, silica gel, or Drierite materials. Such relatively slow reaction with water vapor leads to a measurable degree of device degradation of performance following the sealing of the desiccant inside a device cover due to, for example, moisture absorbed on the inside of a device, moisture vapor present within the sealed device, and moisture permeating through the seal between the device and the cover from the outside ambient. In addition, highly moisture-sensitive electronic devices typically cannot be exposed to moisture levels greater than 1000 ppm even during fabrication and encapsulation, requiring control of the moisture levels until the devices are completely encapsulated. For these reasons control of the moisture level during fabrication and encapsulation is required to prevent degradation of performance.
To reduce the quantity of moisture absorbed on the inside of a device or present within the sealed device, highly moisture-sensitive devices, such as organic light-emitting devices (OLED) or panels, polymer light-emitting devices, charge-coupled device (CCD) sensors, and micro-electro-mechanical sensors (MEMS) are often sealed within a low humidity environment, such as a drybox at humidity levels less than 1000 ppm moisture. To ensure low levels of moisture within the sealed device, these highly moisture-sensitive devices are completely sealed within the low humidity environment prior to any additional processing steps, such as, bonding of interconnects, and module assembly. To achieve this low humidity sealing, highly moisture-sensitive devices, such as charge-coupled device (CCD) sensors and micro-electro-mechanical sensors (MEMS), are typically sealed individually as single elements with separate cover elements after separation from a multiple element substrate or wafer. Other devices, such as organic light-emitting devices (OLED), are sealed as multiple devices on a single element; however, in present manufacturing methods individual cover elements of metal or glass are used to seal each device prior to separation. FIG. 3A shows a typical multiple OLED element 34 containing multiple OLED devices 32 on an individual substrate 10, encapsulated with individual encapsulation enclosures 30 and sealing material 20, and FIG. 3B is a schematic sectional view of the multiple OLED element 34 taken along section line 3Bxe2x80x943B of FIG. 3A. Both of the present methods of sealing highly moisture-sensitive devices require significant levels of handling to assemble individual cover elements to either individual device elements or multiple device elements within a low moisture environment.
To reduce the handling of individual cover elements for encapsulation of multiple highly moisture-sensitive device elements within a low moisture environment, a modification of the LCD sealing method can be envisioned where the sealing material between the substrate and the encapsulation enclosure has no gaps prior to bonding. FIG. 4A shows a highly moisture sensitive electronic device element 14 comprising a substrate 10 containing multiple highly moisture-sensitive electronic devices 12, a single encapsulation enclosure 30 encapsulating all of the highly moisture-sensitive electronic devices 12, and sealing material 20. The problem with this technique is shown schematically in FIG. 4A where the sealing material 20 has been damaged by the high gas pressure inside each seal region produced when the substrate 10 and the encapsulation enclosure 30 are moved to their predetermined spacing after both the substrate and the encapsulation enclosure have contacted the scaling material. This damage typically appears as narrow seal widths or even gaps in the seal, decreasing or eliminating protection of the highly moisture-sensitive electronic devices. FIG. 4B is a schematic sectional view of the highly moisture-sensitive electronic device element 14 taken along section lines 4Bxe2x80x944B of FIG. 4A. It would, therefore, be desirable to have highly moisture-sensitive electronic device elements and a method for fabricating highly moisture-sensitive electronic device elements that does not damage the seals that are required to protect the highly moisture-sensitive electronic devices from moisture during fabrication and encapsulation, and that protects the highly moisture-sensitive electronic devices from moisture during the fabrication process.
Numerous publications describe methods and/or materials for controlling humidity levels within enclosed or encapsulated electronic devices.
For example, Kawami et al., European Patent Application EP 0 776 147 A1 disclose an organic EL element enclosed in an airtight container which contains a drying substance comprised of a solid compound for chemically absorbing moisture. The drying substance is spaced from the organic EL element, and the drying substance is consolidated in a predetermined shape by vacuum vapor deposition, sputtering, or spin-coating. Kawami et al. teach the use of the following desiccants: alkali metal oxides, alkali earth metal oxides, sulfates, metal halides, and perchlorates. Kawami et al., however, do not teach a multiple EL device element with multiple airtight containers nor a method for fabricating a multiple EL device element with multiple airtight containers. The handling and sealing problems and solutions of a multiple EL device element, such as methods to prevent damage to the seal due to high gas pressure inside the seal region during encapsulation, are not discussed nor taught by Kawami et al.
Shores, U.S. Pat. No. 5,304,419, discloses a moisture and particle getter for enclosures which enclose an electronic device. A portion of an inner surface of the enclosure is coated with a pressure sensitive adhesive containing a solid desiccant.
Shores, U.S. Pat. No. 5,401,536, describes a method of providing a moisture-free enclosure for an electronic device, the enclosure containing a coating or adhesive with desiccant properties. The coating or adhesive comprises a protonated alumina silicate powder dispersed in a polymer.
Shores, U.S. Pat. No. 5,591,379, discloses a moisture gettering composition for hermetic electronic devices. The composition is applied as a coating or adhesive to the interior surface of a device packaging, and the composition comprises a water vapor permeable binder which has dispersed therein a desiccant which is preferably a molecular sieve material.
In none of these patents does Shores teach a multiple device element or a method to provide moisture-free enclosures for a multiple device element.
Booe, U.S. Pat. No. 4,081,397, describes a composition used for stabilizing the electrical and electronic properties of electrical and electronic devices. The composition comprises alkaline earth oxides in an elastomeric matrix. Booe does not teach a multiple device element or a method used for stabilizing the electrical and electronic properties of a multiple electrical and electronic device element.
Inohara et al., U.S. Pat. No. 4,357,557, describe a thin-film electroluminescent display panel sealed by a pair of glass substrates for protection from the environment. The method includes a protective liquid introduced between the glass substrates, a spacer positioned for determining the spacing between the pair of substrates, injection holes formed within one of the substrates to withdraw under vacuum the air and gases from the cavity defined by the substrates and to introduce the protective liquid into the cavity, an adhesive adapted to provide bonding between the substrates and the spacer, a moisture absorptive member introduced into the protective liquid, and an adhesive to seal the injection hole. Inohara et al. do not teach a multiple EL device element with multiple airtight containers nor a method for fabricating a multiple EL device element with multiple airtight containers. The handling and sealing problems and solutions of a multiple EL device element, such as methods to prevent damage to the seal due to high gas pressure inside the seal region during encapsulation, are not discussed nor taught by Inohara et al. Although the use of injection holes in one of the substrates will prevent damage to the seal by permitting excess ambient gas to exit through the injection holes during encapsulation, Inohara et al. do not teach this purpose for providing the injection holes. Instead the purpose of the injection holes is to allow introduction of the protective liquid into the cavity defined by the substrates.
Taniguchi et al, U.S. Pat. No. 5,239,228, describe a method for protecting a thin-film electroluminescent device similar to Inohara et al. with the additional feature of a groove in the sealing plate to capture excess adhesive. This groove may also contain a moisture absorption agent. Taniguchi et al. also do not teach a multiple EL device element with multiple airtight containers nor a method for fabricating a multiple EL device element with multiple airtight containers. The handling and sealing problems and solutions of a multiple EL device element, such as methods to prevent damage to the seal due to high gas pressure inside the seal region during encapsulation, are also not discussed nor taught by Taniguchi et al.
Harvey, III et al., U.S. Pat. No. 5,771,562, describe a method of hermetically sealing organic light emitting devices comprising the steps of providing an organic light emitting device on a substrate, overcoating the organic light emitting device with a film of inorganic dielectric material, and sealingly engaging an inorganic layer over the dielectric material. Harvey, III et al. do not teach a multiple OLED device element with multiple airtight containers nor a method for fabricating a multiple OLED device element with multiple airtight containers. Although the inorganic dielectric layer may provide temporary protection from moisture during the encapsulation process, Harvey, III et al. do not teach how this layer can be used to fabricate a multiple OLED device element with multiple airtight containers.
Boroson et al., U.S. Pat. No. 6,226,890, describe a method of desiccating an environment surrounding a highly moisture-sensitive electronic device sealed within an enclosure, including selecting a desiccant comprised of solid particles having a particle size range 0.1 to 200 micrometers. The desiccant is selected to provide an equilibrium minimum humidity level lower than a humidity level to which the device is sensitive within the sealed enclosure. A binder is chosen that maintains or enhances the moisture absorption rate of the desiccant for blending the selected desiccant therein. The binder may be in liquid phase or dissolved in a liquid. A castable blend is formed including at least the desiccant particles and the binder, the blend having a preferred weight fraction of the desiccant particles in the blend in a range of 10% to 90%. The blend is cast in a measured amount onto a portion of an interior surface of an enclosure to form a desiccant layer thereover, the enclosure having a sealing flange. The blend is solidified to form a solid desiccant layer, and the electronic device is sealed with the enclosure along the sealing flange. Boroson et al., however, do not teach a method of desiccating an environment surrounding a multiple highly moisture-sensitive electronic device element sealed within multiple enclosures.
It is the object of the present invention to provide a highly moisture-sensitive electronic device element having highly moisture-sensitive electronic devices and a method for fabrication of said element in which damage of the moisture-sensitive electronic devices within the element due to moisture is prevented and fabrication of said element is simplified over the present art.
In one aspect, this object is achieved by a highly moisture-sensitive electronic device element having highly moisture-sensitive electronic devices comprising:
a) a substrate containing two or more moisture-sensitive electronic devices;
b) an encapsulation enclosure encapsulating all of the highly moisture-sensitive electronic devices on said substrate;
c) sealing material positioned between said substrate and said encapsulation enclosure to form a partial seal between said substrate and said encapsulation enclosure and a space around each moisture-sensitive electronic device or around groups of moisture-sensitive electronic devices; and
d) water absorbing material positioned between said substrate and said encapsulation enclosure and within the space defined by said sealing material.
In another aspect, this object is achieved by a method of making highly moisture-sensitive electronic device elements having a plurality of highly moisture-sensitive electronic devices such as OLED devices on a single substrate wherein the devices are protected from moisture prior to separating the individual devices from the substrate, comprising the steps of:
a) coating a substrate containing two or more highly moisture-sensitive electronic devices with a temporary moisture protection layer; or coating a water absorbing material onto either the substrate or an encapsulation enclosure in positions on the substrate or on the encapsulation enclosure such that after bonding, the water absorbing material will be positioned within each highly moisture-sensitive electronic device or within each group of highly moisture-sensitive electronic devices; or coating both said temporary moisture protection layer and said water absorbing material;
b) placing the sealing material around each highly moisture-sensitive electronic device or around groups of highly moisture-sensitive electronic devices on the substrate or in positions on the encapsulation enclosure such that after sealing the sealing material will be positioned around each highly moisture-sensitive electronic device or around groups of highly moisture-sensitive electronic devices, leaving one or more positions wherein there is a gap not covered by sealing material;
c) disposing the substrate and the encapsulation enclosure, one of which contains the sealing material, in close aligned proximity to each other, but spaced apart, in such aligned proximate position providing an initial ambient pressure;
d) providing relative motion between the substrate and the encapsulation enclosure until the sealing material contacts both the substrate and the encapsulation enclosure, the substrate and the encapsulation enclosure are spaced apart within a predetermined range, and excess ambient gas exits through the gaps but leaving at least portions of the gaps;
e) bonding the sealing material to both the substrate and the encapsulation enclosure;
f) separating the highly moisture-sensitive electronic devices into individual devices or groups of devices having a portion of the initial substrate; and
g) sealing the gaps.
The elements and methods for fabrication of the elements in accordance with the present invention of highly moisture-sensitive electronic device elements element having highly moisture-sensitive electronic devices and methods for their fabrication to prevent premature device failure or premature degradation of device performance provides the following advantages over prior art methods: reduced handling of devices and encapsulation enclosures by sealing all of the highly moisture-sensitive devices on a single substrate as a single element with a single encapsulation enclosure encapsulating all of the highly moisture-sensitive electronic devices on the substrate prior to separating into smaller single or multiple device elements; improved protection from moisture prior to exposure to ambient environments; improved compatibility with automated processes required for high volume manufacturing; improved compatibility with processing inside a low moisture environment; and reduction in encapsulation defects due to pressure differentials inside and outside the highly moisture-sensitive electronic devices.